This invention relates to scanning beam display devices, and more particularly to optical configurations for scanning beam display devices.
A scanning beam display device is an optical device for generating an image that can be perceived by a viewer's eye. Light is emitted from a light source, collimated through a lens, then passed through a scanning device. The scanning device defines a scanning pattern for the light. The scanned light converges to focus points of an intermediate image plane. As the scanning occurs, the focus point moves along the image plane (e.g., in a raster scanning pattern). The light then diverges beyond the plane. An eyepiece is positioned along the light path beyond the intermediate image plane at some desired focal length. An “exit pupil” occurs shortly beyond the eyepiece in an area where a viewer's eye is to be positioned.
A viewer looks into the eyepiece to view an image. The eyepiece receives light that is being deflected along a raster pattern. Light thus impinges on the viewer's eye pupil at differing angles at different times during the scanning cycle. This range of angles determines the size of the field of view perceived by the viewer. Modulation of the light during the scanning cycle determines the content of the image.
For a see-through display, a user sees the real world environment around the user, plus the added image of the scanning beam display device projected onto the retina. When the user looks at an object in the field of view, the eye performs three basic functions. For one function, each eye moves so that the object appears at the center of vision. For a second function, each eye adjusts for the amount of light coming into the eye by changing the diameter of the iris opening. For a third function, each eye focuses by changing the curvature of the eye lens. If the focal distance from the third function does not match the distance to the point of convergence, then the brain detects a conflict. Nausea may occur.